Abrasive material



July 5, 1966 v LIBMAN 3,259,529

ABRASIVE MATERIAL Original Filed Nov. 15, 1963 4 Sheets-Sheet 1INVENTOR.

NELSON A. LIBMAN July 5, 1966 N. A. LIBMAN ABRASIVE MATERIAL 4Sheets-Sheet 2 Original Filed Nov. 15, 1963 Q o mm C 9v mm mwfi m at 8Jim 6 ,I- mm V L L H i g a, mm

W L w mm mm m m w W 1 u R A @N N ow m E N wm Q 6 v m R m Al llfil 5 7MNN mm 0 mm m Q t on m @E aw Afforneys July 5, 1966 N. A. LlBMAN ABRASIVEMATERIAL Original Filed Nov. 15, 1963 INVENTOR.

NELSON A. LIBMAN Attorneys July 5, 1966 N. A. LIBMAN ABRASIVE MATERIAL 4Sheets-Sheet 4 Original Filed NOV. 15, 1963 INVENTOR NELSON A. LIBMANUnited States Patent 3,259,529 ABRASIVE MATERIAL Nelson A. Libman,University Heights, Ohio, assignor to Metal Blast, Inc. Originalapplication Nov. 15, 1963, Ser. No. 334,683. Divided and thisapplication Aug. 18, 1965, Ser. No.

Claims. (Cl. 148-39) This application is a division of application Ser.No. 334,683 for Abrasive Material and Method of Making Same, filedNovember 15, 1963. Application Ser. No. 334,683 is derived fromapplication Ser. No. 53,426 for Method and Apparatus for Making SteelShot, filed September l, 1960, and now Patent No. 3,150,224, and fromapplication Ser. No. 80,505 for Abrasive Material and Method of MakingSame, filed January 3, 1961, and now abandoned. Applications Serial Nos.53,426 and 80,505 are continuation-impart applications of applicationSer. No. 37,885 for Abrasive Material and Method of Making Same, filedJune 22, 1960, and now abondoned.

This invention pertains to steel shot of the type used in blast cleaningcastings and the like.

In many manufacturing processes metal bodies, such as steel castings,are treated by impinging metal shot against surfaces of the body. Inblast cleaning, the body being treated is placed in a suitable containerand metal pellets known as shot are impinged against the surfaces of thebody. The impingement is usually obtained either by entraining the shotin a blast of air to project the shot, or by mechanical means projectingthe shot, against the body. This art is known generally as metalblasting, or shot blasting, and will be referred to here by these terms.

The types of shot used in metal blasting usually are classified as iron,malleable or steel. The malleable shot is superior to chilled iron-interms of life characteristics and steel is, of course, superior tomalleable. At the same time, the cost of chilled iron shot is quite low,the malleable more expensive than the chilled iron, and the steel,heretofore, has been quite expensive.

Generally speaking, most manufacturing techniques can be satisfactorilyperformed with any one of the three classes of shot. Accordingly, theshot is usually selected for a given job on a basis of cost ofsuificient shot of the selected type to do the job.

The purpose of the present invention is to provide new and improvedsteel shot of very high and uniform quality which is produced at a costcomparable to the cost of producing malleable shot. The steel shot ofthis invention is made in such a manner that standards of quality can bemaintained over both large and small production runs so that theresultant product has superior characteristics.

As generally contemplated by the invention, iron shot, which is usuallyformed by a quenching process, is heated to a temperature which is highenough to cause the carbon in the shot to migrate. The temperature ismaintained below the fusing temperature of the iron shot. A flow ofoxygen is passed over the shot while it is simultaneously tumbled andmaintained at the described temperature. This oxygen flow is continueduntil enough of the migrating carbon has been oxidized to reduce thecarbon content in the shot to less than 1.7% by weight and preferablywell below 1%.

A specific method of production hereinafter described in more detailcontemplates the initial step of melting gray iron in a cupola. The grayiron is then formed into a stream which is dispersed, as by a blast ofair, to separate the stream into a plurality of drops. The drops arethen caught in a quenching tank to produce chilled iron pellets. Thesechilled iron pellets are sorted or graded into groups, each of whichincludes pellets of substantially uniform size.

Patented July 5, 1966 The pellets of one group are then placed into afeed bin. They are continuously gravity fed from the feed bin into afirst tube which is an elongated cylindrical member open at both ends.The shot pellets are annealed in the tube as they are passing throughit. The pellets then pass from the first tube outlet through a gravityconveyor to an inlet of a second tube. The second tube is formed of amaterial which has less afiinity for oxygen at the temperatures underconsideration than does the carbon in the pellets. As the pellets arepassed through the second tube, they are heated to a temperature of atleast 1650 F. and below the fusing point of the pellets. They aremaintained in the second tube until the carbon content is less than 1.7%by weight. Thereafter, the pellets are gravity fed to a water-cooledtube for air cooling or water quenching depending upon the hardnessdesired.

The resulting shot is characterized by a long life, abrasion resistance,and a relatively high sulphur content. The shot is further characterizedby a substantial carbon gradient increasing from a tough, hypoeutectoidouter surface to a relatively hard, hypereutectoid core.

A fuller understanding of the invention and of the novel and improvedcharacteristics of the steel shot which is provided will be had byreference to the following description taken in conjunction with theaccompanying drawings.

In the drawings:

FIGURE 1 is a side elevational view, the parts being broken away andremoved for clarity of detail, of an apparatus for manufacturing steelshot in accordance with this invention;

FIGURE 2 is cross-sectional view of the apparatus taken on the line 22of FIG. 1;

FIGURE 3 is an enlarged, fragmentary view taken on the line 33 of FIG.2;

FIGURE 4 is a cross-sectional view taken on the line 44 of FIG. 3;

FIGURE 5 is a diagrammatic view of the apparatus and the controls;

FIGURE. 6 is a photomicrographic illustration of a a central portion ofa shot pellet made in accordance with this invention; and,

FIGURE 7 is a photomicrographic illustration of a portion near thesurface of one of the shot pellets made in accordance with thisinvention.

As generally described above, the steel shot of this invention may beproduced by first forming a plurality of chilled iron pellets. Thepreferred method for forming the chilled iron pellets is to melt aquantity of gray iron in a cupola. The melted iron is then poured fromthe cupola into a stream. The stream is separated andbroken into dropsof appropriate size by any of several known and accepted techqniques.This may be accomplished by a blast of air, water, or other fluid, or bymechanical means. The drops are caught in a quenching tank where thechilling action of the Water solidifies the drops into chilled ironpellets or shot. The resultant chilled iron pellets are brittle andshort lived if used as shot. They have a carbon content which is usuallyin excess of 3%.

As the next preferred step, the shot is graded into size to sort outthose of suitable size for use as metal blasting shot. Any shot which istoo large to pass through the screen with 0.078" openings is comminutedto break it into particles of suitable size. The comminuted particlesare also sorted into shot of appropriate sizes.

A group of shot pellets of a selected size are next heated to atemperature which is below the fusion point of the pellets butsufiiciently high to cause the carbon in the shot pellets to migrate.excess of about 1650 F. with the fusing temperature being about 2060 F.to 2200 F., depending on the shot This temperature usually is in' size.The heating is preferably accomplished in a continuous manner by passinga quantity of burned natural gas laden with hot air over the shot.Simultaneously, the shot is tumbled to expose the entire surface of eachpellet to the passing, hot air-ladened gas. The tumbling and the passageof gas is continued for a period of from about 18 minutes to 45 minutes,depending upon the selected temperature, the shot size, and the amountof oxygen available in the gas passed over the shot. This step of theprocess is continued until the carbon has been lowered to less than 1.7%by weight in each of the pellets. Preferably, the carbon is loweredbelow 1%.

Reference is now made to R168. l-5 of the drawings which illustratesuitable apparatus for continuously heat ing the chilled iron pelletsand converting the pellets into steel shot. As shown most clearly inFIG. 1, a feed bin 11 is provided. The chilled iron pellets arecontinuously fed to the him by a conveyor 11. A supply of pellets,indicated generally by reference numeral 12, are continuously gravityfed from the bin through a pellet nozzle 13. The pellet nozzle 13continuously delivers a supply of the chilled iron pellets to the inletend 1 3. of an anneal ing tube 15.

A pair of burner nozzles 17 are positioned adjacent the inlet end 14 ofthe annealing tube 15. A suitable fuel, such as natural gas mixed withan appropriate quantity of air, is directed from each of the nozzles 17to provide a continuous flow of hot gas through the tube 15. The flow ofhot gas both heats the pellets and pro pels them through the tube 15.

As the pellets are propelled from the tube through its outlet end 18,they are trapped by a combination deflection bafile and hood 19. A hoodoutlet 20 is provided to conduct the gravity fed flow of pellets throughan inlet end 21 of a second and lower tube 22. The lower tube 22 is acarbon removal tube.

The carbon removal tube 22 has another pair of nozzles 23 positionedadjacent its inlet end 21. These nozzles 32 provide a continuous blastof air and fuel which is burned in a manner similar to fuel projected bythe annealing tube nozzle 17. The pellets are projected through thecarbon removal tube 22 until they come out the outlet end 24. From theoutlet end 24 of the tube 22, the pellets enter another combination hoodand deflection baflle 25.

The pellets coming out of the outlet end 24 of the carbon removal tube22 are steel pellets. These steel pellets or shot are gravity fedthrough a conduit 26 into a cooling tube 27. The steel pellets areair-cooled within the cooling tube 27 which, in turn, is continuouslycooled by a water bath provided by an elongated spray nozzle 28. Thepellets also may be quenched in a tank 79 (FIG. 5) or subjected to awater spray for quick cooling.

Each of the tubes through which the pellets pass are shown to have aplurality of annular support collars. These annular support collars aredesignated by reference numerals 30, 31, 32 on the tubes 15, 22, 27,respectively. A plurality of sup-port wheels 33, 34, 35 are provided forthe tubes 15, 22, 27, respectively. The support wheels 33, 34, 35 arerespectively journaled at 36, 37, 38 on a frame 40. As is best shown inFIG. 2, the support wheels 33, 34, 35 are provided in pairs such thateach one of the collars 30, 31, 32 rides on an associated horizontallyspaced pair of support wheels 33, 34, 35, respectively. In this manner,the tubes 15, 22, 27 are rotatably supported on the frame 4%.

Motors 41, 42, 43 are mounted on the frame and suitably connected to thetubes 15, 22, 27 to cause relative rotation of the frame and tubes. Inthe embodiment shown, all of the motors drive the tubes with chains andsprockets shown at 44, 45, 46, respectively.

In the case of the annealing tube 15, a very satisfactory member can bemade within a single, one-piece, cast steel, tubular cylinder. Theplurality of inlet guide baffies 49 are provided in the interior of thetube adjacent the inlet 14 to assist in directing the pellets into theinterior of the annealing tube 15. A series of elongated agitationbaflles 5% are in the tube and they extend from near the inlet end 14 tothe outlet end 18 to agitate the pellets in the tubes as the device isused.

The construction of the carbon removal tube 22 differs in constructionfrom the annealing tube 15. As shown, the carbon removal tube 22includes an inner sleeve liner 51. This sleeve liner is formed of amaterial having a carbon-free work surface. The term carbomfree isintended to mean a material having a work surface that is carbon-freerelative to the minimum carbon content desired in the steel shotproduced. That is to say, the worl; surface of the liner 51 has a carboncontent which is at least equal to and preferably less than the minimumcarbon content desired in the steel shot.

The preferred material for the sleeve liner 51 is a carbon-freestainless steel. The liner 51 may be formed of a stainless steelmaterial which initially has a work surface with an excess of carbonabove the desired minimum carbon content of the steel shot, and themechanism operated for a time, with or without pellets passing throughit in the manner described, to decarburize the liner 51.

The material of the liner 51 must, as indicated above, have a worksurface which is carbon-free relative to the steel shot produced. Itmust also be capable of withstanding up to the fusing temperature of thepellets. This fusing temperature will be in the neighborhood of 2250 F.,depending upon the size and chemical content of the particular pellets.It is also essential that the sleeve liner 51 be formed of a materialwhich has less affinity for oxygen than does carbon in the temperatureranges to which the liner will be subjected, namely, from about 1650 F.to the fusing point of the pellets. The work surface of the liner 51must also have good abrasion resistance to withstand the eroding actionof the pellets passing therethrough. Obviously, other materials whichhave these described characteristics may be substituted for thepreferred carbon-free stainless steel.

The carbon removal tube 22 is also shown as being provided with aplurality of inlet baffles 53 adjacent the inlet end 21. The inletbafiles 53 correspond and function to the inlet bafiles 49 of theannealing tube 15. Agitation bafiies 54 which correspond in function andgeneral construction to the agitation bafiies are also provided in thecarbon removal tube 22. The bafiles 53, 54 of the carbon removal tubeare formed of a carbon-free material capable of withstanding thetemperatures found in the tube and having less afiinity for oxygen atthose temperatures than does the carbon in the shot. These bafiles, likethe work surface of the sleeve liner 51, need not be completelycarbon-free at the time of installation, but will be made so when theapparatus is operated according to the described process.

The burners 17 are supplied by suitable conduits 60. The conduits 69 maybe supplied by suitable mixing valves 61, or, in the alternative,connected directly to suitable fuel and air supplies. In the arrangementshown, a supply of air under pressure 62 is connected to the mixingvalve 61 by a conduit 63. Valves 64 are provided to control the pressureand volume of air supplied to the mixing valves 61. Fuel under pressure,preferably natural gas, is supplied by a source 65. The gas and fuel isconducted by conduits 66 to the mixing valves 61. The pressure andvolume control valves 67 are in the conduit 66 and control the quantityand pressure of the gas supplied to the mixing valves.

To control the temperature in the carbon removal tube 33 and the rate offlow of shot through the tube, controls for the nozzles 23 are providedwhich are similar to the controls for the nozzle 17. Thus, conduits 40conduct mixed gas and air from mixing valves 71. Mixing valves 71 aresupplied air under pressure from a suitable source 72 by conduits 73..Volume and pressure control valves 74 control the air supplied to themixing valves 71. Fuel under pressure is supplied by a source 75 to themixing valves by conduit 76. Volume and pressure control valves 77 areprovided to control the quantity of pressure of the fuel.

Improved carbon removal characteristics are obtained if the air isenriched with extra oxygen. Oxygen is supplied from a source 85 which iscontrolled by a valve 86 and connected to the air supply conduit 73.

The operation of the described apparatus will be best understood byreference to FIG. 5. As generally described above, chilled iron shotpellets are continuously fed from the bin through the pellet nozzle 13into the annealing tube 15. The pellets are blown through the annealingtube by the blast of burned natural gas or other fuel emitted by thenozzles 17. As the pellets pass through the tube 15 they are agitated bythe bafiles 50 as the tube 15 continuously rotates. The agitationexposes all of the pellets to the hot gases emitted by the nozzles 17and thus assures uniform heat treatment of each of the pellets.

It should be noted that while the tube 15 is identified as an annealing.tube and while the process which occurs in that tube is an annealingaction, one of its principal purposes in the process is to preheat thepellets prior to their conduction into the carbon-removal tube 22. Thepellets, as they are emitted from the annealing tube 15, will be chillediron pellets that are partially, if not completely, transformed intomalleable iron shot.

The valves 64, 67 are adjusted so that the gases emitted by the nozzle17 maintain the temperature of the pellets in the annealing tube 50 in arange of from about 900 F. to about 1200 F. The pellets are conveyedthrough the tube 15 by this flowing consumed fuel and air mixture in atime range of from about 9 to 22 minutes.

The pellets are conveyed from the outlet end 18 of the annealing tube 15and immediately and while still hot are fed into the inlet 21 of thecarbon-removal tube 22. The pellets are conveyed through thecarbon-removal tube 22 in a time range of from about 9 to 22 minutes andat a temperature of from about 1650 F. to the fusing point of thepellets which, as previously noted, will be about 2250" F.

As will be apparent from the foregoing description, the carbon-removaltube 22, and more particularly the carbon-free work surface of the liner51, has less afiinity for hot oxygen than does the carbon in the shotentering the carbon-removal tube from the annealing tube 15, Thus, whenthe pellets are conveyed through the carbonremoval tube 22 at the speedand temperature described, the carbon in the pellets tends to migrate totheir surfaces. As the hot oxygen-laden air passes over the surfaces ofthe pellets, the carbon is oxidized or burned off, thus converting theannealed shot to steel shot. With the pellets maintained in the tube forthe indicated period of time and under the described conditions, thecarbon is lowered to less than 1.7% by weight in each of the pellets andpreferably is lowered to less than 1%. Adjustment of the valves 74, 77and therefore the volume of the air and fuel supply is used to controlthe temperature and rate of flow of the pellets and thus to obtain thisdesired end.

According to the preferred process, the pellets are aircooled in thetube 27 after the migrating carbon in the pellets has been burned off toreduce the carbon content to less than 1.7%. If desired, the pellets canalso be quenched and/or water cooled in the tank 79 to increase thehardness of the steel shot produced.

Since the process is continuous, periodic samplings of the finishedproduct may be made to provide an excellent, practical application ofstatistical quality control. Samples periodically taken can beimmediately subjected to suitable testing, such as a centrifugal, impacttest, to determine the physical properties of the product. If theproduct in any given sample is slightly varied from the desired product,adjustment may be made in the air and fuel supplies to improve thecharactertistics.

The product produced has unusual and outstanding characteristics. As canbe seen in the photomicrographs, there is a substantial gradient ofcarbon increasing from the outer surface of the pellet to the core.Preferably, the surface of the pellet is hypoeutectoid and the core ishypereutectoid. Thus, a soft, ductile, tough outer surface and arelatively hard core are formed.

The product produced by the previously described process is extremelytough and durable, has exceptional wear characteristics, and a very longabrasion life. The shot so produced is readily discernible from priorknown metal shot because it has a different chemical analysis.

Schedule A sets out broadly and Schedule B in more detail suitablequantities of ingredients in metal shot made in accordance with theteaching of this invention:

SCHEDULE A Material: Percentage by weight Carbon Less than 1.7.Phosphorous From about 0.2 to .90. Sulphur From about 0.10 to about0.25.

Iron, alloying materials and impurities Remainder SCHEDULE B Material:Percentage by weight Carbon Less than 1.7. Manganese From about 0.25 toabout: 0.75. Phosphorous From about 0.02 to about 0.90. Sulphur Fromabout 0.10 to about 0.25. Silicon From about 0.20 to about 2.0. Thebalance Substantially all steel alloy.

The steel alloy making up the balance will, of course, be predominantlyiron. Other alloying material such as copper, chrome and impurities maybe present. A typical formulation of a shot pellet made in accordancewith this teaching is as follows:

For economic reasons, it is impractical to employ a highly-alloyed ironand hence the process has been limited to low-alloy irons, i.e., ironhaving less than 10% by weight alloying elements. Further, it is notpractical to employ this method with impurities other than phosphorousor sulphur being greater than 3 /2 With a greater amount of impurities,the iron does not become satisfactory shot.

EXAMPLE As a specific example, the shot used will be capable of passingthrough a screen with an 0.078 inch opening. With shot, for example, ofapproximately 0.033 inch size, the shot will be passed through anannealing tube of 2 feet in diameter and 18 feet in length at about 2tons to about 3 tons per hour and preferably at about 3 tons per hour.To propel shot through the annealing tube at this rate, air at fromabout 150 to about 300 cubic feet per minute and preferably about 300will be fed to the burners 17. Natural gas is mixed with the air toprovide an adequate supply of consumed gases at the temperaturesdescribed. There are from about 8 to 11 parts of air to one of gas andpreferably about 11. The pressure of the natural gas will be from about6 ounces to about 8 ounces and preferably about 8 ounces, while thepressure of the air will be from 15 ounces to ounces and preferablyabout 20 ounces.

After the shot has passed through the annealing tube of this example, itwill be conveyed to a carbon removal tube of about 2 feet in diameterand about 18 feet in length at about 2 tons to about 3 tons per hour andpreferably at about 3. To propel shot through the carbon removal tube atthis rate, air at from about 150 to about 300 cubic feet per minute andpreferably about 300 cubic feet per minute is fed to the burners 23.This air is mixed with natural gas in the same ratios as in the burners17 to provide an adequate supply of oxygen-laden, consumed gases at thetemperatures described. The pressure of the natural gas will be fromabout 6 ounces to about 8 ounces and preferably about 8 ounces, whilethe pressure of the air will be from 15 ounces to 20 ounces andpreferably about 20 ounces.

Oxygen is added, if desired, at up to 80 cubic feet a minute, preferablyabout 10 parts of oxygen are added to one of air. Thus, under thedescribed preferred con ditions 30 cubic feet per minute of oxygen areadded to the mixture. This is especially important with larger size shotwhere relatively large amounts of oxygen are needed.

While this invention has been described with considerable detail, it isbelieved that itessentially comprises a novel and improved steel shotcharacterized by a carbon content of less than 1.7%, a phosphorouscontent of from .02 to 0.90%, and a sulphur content of from 0.10 to0.25%. The invention also comprises a shot structure characterized by aductile hypoeutectoid surface and a relatively harder, hypereutectoidcore.

Many modifications and variations of the invention will be apparent tothose skilled in the art in View of the foregoing detailed disclosure.Therefore, it is to be understood that, within the scope of the appendedclaims, the invention can be practiced otherwise than as specificallyshown and described.

What is claimed is:

1. An abrasive steel shot particle of a ferrous alloy characterized by asubstantial carbon gradient increasing from a tough, hypoeutectoid outersurface to a relatively hard, hypereutectoid core, and including thefollowing parts by weight:

Material: Percentage by weight Carbon Less than 1.7. Phosphorous Fromabout .02 to .90. Sulphur From about 0.10 to about 0.25

2. A11 abrasive steel shot particle of ferrous alloy characterized by amaximum size of approximately .078 inch and a substantial carbongradient increasing from a tough, hypoeutectoid outer surface to arelatively hard, hypereutectoid core, and including the following partsby weight:

Material: Percentage by weight Carbon Less than 1.0. Phosphorous Fromabout .02 to .90. Sulphur From about 0.10 to about 0.25.

Material: Percentage by weight Carbon From about .03 to about 1.7.Phosphorous From about 0.02 to about 0.90. Sulphur From about 0.10 toabout 0.25. Alloying metals From about .23 to about 10.0.

Iron and impurities Balance. 4. An abrasive steel shot particle of aniron carbon alloy having a carbon content less than 1.7% by weight, saidparticle having a maximum size of .078 inch and a substantial carbongradient increasing from a tough, hy- I poeutectoid surface to arelatively hard, hypereutectoid core.

5. An abrasive steel shot particle of an iron carbon alloy having acarbon content less than 1% by weight, said particle having a maximumsize of approximately .078 inch. and a substantial carbon gradientincreasing from a tough, hypoeutectoid outer surface to a relativelyhard, hypereutectoid core.

References Cited by the Examiner UNITED STATES PATENTS 2,182,805 12/1939Hagenbuch et al. 148-39 X 2,863,790 12/1958 Chen 148--36 X 2,867,5541/1959 Wilson et al 148126 X DAVID L. RECK, Primary Examiner.

C. N. LOVELL, Assistant Examiner.

3. AN ABRASIVE FERROUS ALLOY SHOT PARTICLE CHARACTERIZED BY A MAXIMUMSIZE OF APPROXIMATELY .078 INCH AND BYA SUBSTANTIAL CARBON GRADIENTINCREASING FROM A TOUGH, HYPOEUTECTOID OUTER SURFACE TO A RELATIVELYHARD, HYPEREUTECTOID CORE, AND CONSISTING ESSENTIALLY OF THE FOLLOWINGMATERIALS IN THE FOLLOWING PROPORTIONS: MATERIAL: PERCENTAGE BY WEIGHTCARBON FROM ABOUT .03 TO ABOUT 1.7. PHOSPHOROUS FROM ABOUT 0.02 TO ABOUT0.90. SULPHUR FROM ABOUT 0.10 TO ABOUT 0.25. ALLOYING METALS FROM ABOUT.23 TO ABOUT 10.0 IRON AND IMPURITIES BALANCE.